A relief printing plate is generally composed of a support such as a metal or plastic substrate, and a relief-formed resin layer arranged thereon. Examples of a method of preparing a relief printing plate in which irregularities are formed on a resin layer as a relief include the following:                i) a method of forming a relief by exposing a photosensitive resin layer, on which an image can be formed, to UV light through a negative film; selectively curing an image part; and then removing uncured part using a developer (analog platemaking),        ii) a method of forming a relief by arranging a laser-sensitive mask layer element capable of forming an image mask on a photosensitive resin layer on which an image can be formed; irradiating thereto a laser beam based on image data controlled by a digital device; forming an image mask from the mask layer element at this point; subsequently exposing the resultant to UV light through an image mask; selectively curing an image part; and then removing uncured part using a developer (CTP platemaking), and        iii) a method of forming irregularities as a relief by engraving a resin layer with a laser beam (laser engraving platemaking).        
The thus obtained plate is immobilized on a plate cylinder of a printing machine using a double-sided adhesive tape, a magnet or the like or by vacuuming and subsequently subjected to printing. Therefore, during the plate-making (especially during development) as well as printing, the support and the resin layer should never be detached from each other. In addition, for storage of the thus printed plate for re-printing, it is required that the support and the relief be firmly adhered to each other such that the relief does not peel off from the support when the printed plate is removed from the plate cylinder.
As a method of adhering a support with a relief-forming resin, it has been proposed to arrange a variety of intermediate layers between the support and the resin layer. Japanese Patent Application Laid-Open Publication (JP-A) No. 2008-181059 discloses a method of adhering a photosensitive resin layer, which yields a relief, and a support using a copolymerized polyester resin and a polyfunctional isocyanate. JP-A No. 2007-224093 discloses a method of adhering a photosensitive resin layer, which yields a relief, and a support using an intermediate layer comprising a carboxyl group-containing polymer and an oxazoline group-containing polymer. JP-A No. H11-231546 discloses a method where two intermediate layers, which are a first intermediate layer having good adhesion with a support and a second intermediate layer comprising a reactive group-containing compound for improvement of the adhesion with a photosensitive resin layer that yields a relief, are arranged.
In a prior art method using a reactive compound as an intermediate layer to adhere a support and a relief-forming resin layer, the reactive compound may be deactivated during storage of the resulting printing plate original or printing plate and the adhesive strength is thereby weakened, causing a defect that the relief peels off from the support during platemaking or printing.
It could therefore be helpful to provide a way to inhibit peeling between a support and an image-forming resin layer.